Adjustable spacer assemblies are used in many contexts. They may be used to fill space in order to secure an item against motion within a container. When a spacer is used, it may replace or supplement the use of packing material. Adjustable spacer assemblies may be used for furniture leveling. Adjustable spacer assemblies are used in orthopedic surgery in such applications spinal fusion to fill space between adjacent vertebrae surrounding a missing vertebra. Adjustable spacer assemblies may be used to set the height of a worktable or load-bearing surface.
Various shortcomings of the prior art include lack of flexibility in performance or complexity in construction. U.S. Pat. No. 5,924,661, in describing the background of the invention, refers to a prior art mechanism for leveling items such as heavy machinery. A pair of freely sliding opposed wedges are interconnected for movement by a threaded shaft. Further described are a number of approaches to furniture stabilizing that suggest the use of a combination of wedges having ridges that intermesh with each other for adjustable stability. Mechanisms simply using two opposed wedges with forces applied to a threaded shaft parallel to long, flat surfaces of the wedges do not make the most efficient use of force applied to the wedges. Such mechanisms also tend to bind. Forming ridges in wedges creates additional expense in manufacture.
In orthopedic surgery, a number of adjustable intervertebral implants have been provided. One such implant is disclosed in U.S. Pat. No. 6,176,882. A mechanism for varying the height of the implant is housed between fixed sidewalls. The mechanism includes first and second wedges which are moved horizontally by a threaded bolt to displace third and fourth wedges vertically. Aspects of complexity of this apparatus include the requirement to have opposite ends of the bolt formed with a left hand thread and a right hand thread respectively. U.S. Pat. No. 6,368,351 includes an intervertebral implant assembly in which a cylinder on a threaded bolt is displaced as the bolt turns to cam against two facing slanted surfaces included in upper and lower members respectively. The upper and lower members are hinged at one end. This mechanism only tilts the upper and lower members with respect to each other. It does not displace both ends of the upper and lower members from each other.
U.S. Pat. No. 6,889,946 discloses a leveling shoe that includes first and second wedge members that are moved to adjust the height of a support plate having wedges formed on its lower surface. U.S. Pat. No. 6,463,114 discloses a jacking device which includes a central threaded wedge member that bears against surrounding wedge members to produce relative movements. These patents exemplify the prevalent practice of using different structures for different applications. These structures are not “universal” in application. While no structure is truly universal, the term universal may be applied to a device which has a wide range of applications.